diff --git a/flytekit/core/container_task.py b/flytekit/core/container_task.py
index 1b078f83a7..7773226c1a 100644
--- a/flytekit/core/container_task.py
+++ b/flytekit/core/container_task.py
@@ -112,14 +112,18 @@ def _get_data_loading_config(self) -> _task_model.DataLoadingConfig:
             io_strategy=self._io_strategy.value if self._io_strategy else None,
         )
 
+    def _get_image(self, settings: SerializationSettings) -> str:
+        if settings.fast_serialization_settings is None or not settings.fast_serialization_settings.enabled:
+            if isinstance(self._image, ImageSpec):
+                # Set the source root for the image spec if it's non-fast registration
+                self._image.source_root = settings.source_root
+        return get_registerable_container_image(self._image, settings.image_config)
+
     def _get_container(self, settings: SerializationSettings) -> _task_model.Container:
         env = settings.env or {}
         env = {**env, **self.environment} if self.environment else env
-        if isinstance(self._image, ImageSpec):
-            if settings.fast_serialization_settings is None or not settings.fast_serialization_settings.enabled:
-                self._image.source_root = settings.source_root
         return _get_container_definition(
-            image=get_registerable_container_image(self._image, settings.image_config),
+            image=self._get_image(settings),
             command=self._cmd,
             args=self._args,
             data_loading_config=self._get_data_loading_config(),
diff --git a/flytekit/core/python_auto_container.py b/flytekit/core/python_auto_container.py
index c43e3d4d14..7099456e5b 100644
--- a/flytekit/core/python_auto_container.py
+++ b/flytekit/core/python_auto_container.py
@@ -175,6 +175,13 @@ def get_command(self, settings: SerializationSettings) -> List[str]:
         """
         return self._get_command_fn(settings)
 
+    def get_image(self, settings: SerializationSettings) -> str:
+        if settings.fast_serialization_settings is None or not settings.fast_serialization_settings.enabled:
+            if isinstance(self.container_image, ImageSpec):
+                # Set the source root for the image spec if it's non-fast registration
+                self.container_image.source_root = settings.source_root
+        return get_registerable_container_image(self.container_image, settings.image_config)
+
     def get_container(self, settings: SerializationSettings) -> _task_model.Container:
         # if pod_template is not None, return None here but in get_k8s_pod, return pod_template merged with container
         if self.pod_template is not None:
@@ -187,11 +194,8 @@ def _get_container(self, settings: SerializationSettings) -> _task_model.Contain
         for elem in (settings.env, self.environment):
             if elem:
                 env.update(elem)
-        if settings.fast_serialization_settings is None or not settings.fast_serialization_settings.enabled:
-            if isinstance(self.container_image, ImageSpec):
-                self.container_image.source_root = settings.source_root
         return _get_container_definition(
-            image=get_registerable_container_image(self.container_image, settings.image_config),
+            image=self.get_image(settings),
             command=[],
             args=self.get_command(settings=settings),
             data_loading_config=None,
diff --git a/flytekit/remote/remote.py b/flytekit/remote/remote.py
index 4fd17fe40b..aad5adbd3f 100644
--- a/flytekit/remote/remote.py
+++ b/flytekit/remote/remote.py
@@ -986,6 +986,7 @@ def register_script(
                 destination_dir=destination_dir,
                 distribution_location=upload_native_url,
             ),
+            source_root=source_path,
         )
 
         if version is None:
diff --git a/plugins/flytekit-spark/flytekitplugins/spark/task.py b/plugins/flytekit-spark/flytekitplugins/spark/task.py
index 39a93afd06..079cf8815c 100644
--- a/plugins/flytekit-spark/flytekitplugins/spark/task.py
+++ b/plugins/flytekit-spark/flytekitplugins/spark/task.py
@@ -7,6 +7,7 @@
 from flytekit import FlyteContextManager, PythonFunctionTask, lazy_module, logger
 from flytekit.configuration import DefaultImages, SerializationSettings
 from flytekit.core.context_manager import ExecutionParameters
+from flytekit.core.python_auto_container import get_registerable_container_image
 from flytekit.extend import ExecutionState, TaskPlugins
 from flytekit.extend.backend.base_agent import AsyncAgentExecutorMixin
 from flytekit.image_spec import ImageSpec
@@ -136,6 +137,13 @@ def __init__(
             **kwargs,
         )
 
+    def get_image(self, settings: SerializationSettings) -> str:
+        if isinstance(self.container_image, ImageSpec):
+            # Ensure that the code is always copied into the image, even during fast-registration.
+            self.container_image.source_root = settings.source_root
+
+        return get_registerable_container_image(self.container_image, settings.image_config)
+
     def get_custom(self, settings: SerializationSettings) -> Dict[str, Any]:
         job = SparkJob(
             spark_conf=self.task_config.spark_conf,